In the past, there has been proposed a power supply device which converts power inputted from an external power supply and outputs converted power and includes a thermistor having a positive temperature property (so-called a PTC thermistor) in order to suppress rush current at the time of activation interposed in a power supply path from such a power supply (e.g., see document 1 [JP 2008-104273 A]). In this regard, when excess current such as rush current flows, Joule heat causes a rise in temperature of the thermistor, and this leads to increase in a resistance of the thermistor. Consequently, such current can be suppressed. The thermistor may have such a temperature property that resistance greatly varies with temperature. For example, a resistance of the thermistor at 160° C. is approximate 100 times as high as a resistance of the thermistor at 25° C.
Further, a thyristor is connected in parallel with the aforementioned thermistor and a circuit of the power supply device is configured to keep the thyristor on during stable operation. Rush current is likely to occur only at the time of activation. Therefore, to avoid loss caused by the thermistor, a current is made to flow through the above thyristor during stable operation.
Further, there has been proposed a power supply device including multiple buck converters connected in parallel together between output ends of a DC power supply circuit (e.g., see document 2 [JP 2011-78218 A]). For example, a load such as a light emitting diode array is connected between output ends of each buck converter. The aforementioned DC power supply circuit may be, for example, a capacitor for smoothing a pulsating output of a diode bridge, a conventional boost converter, or the like. In this power supply device, the multiple buck converters can share the DC power supply circuit, but can be different from each other in specifications and operations.
The power supply device including the DC power supply circuit and the multiple buck converters as with document 2 can be modified so that the parallel circuit of the thermistor and the thyristor is interposed in the power supply path to the DC power supply circuit as with document 1.
With regard to the power supply device as modified above, it is assumed that the circuit of the power supply device is designed so that the thyristor is kept on while any of the buck converters operates stably. In this case, even if in one or some of buck converters a switching element may be short-circuited and excess current may flow, the thermistor cannot provide effects of suppression of current while the other(s) of buck converters operates stably.